1. Field of the Invention
The present invention relates to heat exchanger evaporators, especially to a counterflow evaporator optimized for zeotropic refrigerants having significant glide characteristics. In particular, the invention relates to a shell and tube type evaporator, where the refrigerant flows through the tubes and evaporates, while a fluid flows through the shell and is cooled by the evaporating refrigerant. The evaporator is a component of a refrigeration system which can be used for cooling large quantities of water.
2. Description of Related Art
Refrigeration systems of the type used to cool large quantities of water typically include a heat exchanger evaporator having two separated passageways. One passageway carries refrigerant, and another carries the fluid to be cooled, usually water. As the refrigerant travels through the evaporator, it absorbs heat from the fluid and changes from a liquid to a vapor phase. After exiting the evaporator, the refrigerant proceeds to a compressor, then a condenser, then an expansion valve, and back to the evaporator, repeating the refrigeration cycle. The fluid to be cooled passes through the evaporator in a separate fluid channel and is cooled by the evaporation of the refrigerant. The fluid can then be routed to a cooling system for cooling the spaces to be conditioned, or it can be used for other refrigeration purposes.
One method of increasing the efficiency of heat exchanger evaporators in general, especially those of shell and tube type, is to vary the number and the dimensions of the tubes carrying the refrigerant. This approach, however, results in a prohibitive cost increase.
Another approach used to increase the efficiency of heat exchangers in general has been to install rods in heat exchanger tubes, to form annular passages within which a fluid flows. Applications of this approach are disclosed in U.S. Pat. No. 1,303,107 to Oderman; U.S. Pat. No. 3,749,155 to Buffiere; and U.S. Pat. No. 5,454,429 to Neusauter. This approach increases heat transfer through the outer wall of the annulus by increasing refrigerant flow rate near the wall. However, this approach often has drawbacks. For example, galvanic corrosion between metal parts made of different metals can cause premature failures of the heat exchanger and require excessive maintenance and repairs. When the rods are used within the tube passages, the energy of the flow can cause the rods to vibrate. The acoustic energy developed by the interaction between the flow and the rods in the tubes can damage the structure of the evaporator over time. In some application, this approach causes a high pressure drop across the tube, thereby reducing the efficiency of the refrigeration cycle. Moreover, applications of this approach often have increased the costs of the resultant heat exchanger substantially, because of the material costs of the rod and the material and labor costs associated with installing and holding the rod within the tube.
Recently, certain regulatory bodies have placed restrictions on the types of refrigerants that can be used in certain refrigeration applications. In view of these restrictions, along with the above limitations on existing evaporator designs, there continues to exist a need for an improved evaporator for refrigerants.
Accordingly, an object of the present invention is to provide an evaporator for a refrigeration cycle that addresses the problems, limitations, and disadvantages of presently used evaporators of all types, particularly those used in air cooled chiller units.
Another object is to provide an evaporator that efficiently operates with newer refrigerants, particularly zeotropic refrigerants with glide characteristics.
Yet another object is to provide an improved evaporator that is made of inexpensive components and is economical to build.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and obtained by the apparatus and combinations particularly pointed out in the written description and claims hereof, as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the invention as embodied and broadly described, the invention includes a heat exchanger assembly comprising a tubular elongated member, an elongated inner member disposed within the elongated tubular member, both members being dimensioned to form an annulus between the opposing surfaces of the inner and tubular members. This annulus facilitates heat transfer between a refrigerant flowing in the annulus and a fluid flowing over the tubular member. The assembly also includes a plurality of resilient support members, spaced along the length of the inner member and protruding from the inner member, to engage the tubular member and support the inner member concentrically within the tubular member. The support members preferably are tufts, most preferably tufts that are made of clusters of bristles fabricated integrally with the inner member.
Preferably, a plurality of the heat exchanger tube assemblies are held within a shell of an evaporator, with each assembly having a length determined according to the amount of heat being exchanged. The resultant evaporator preferably is used to transfer heat between a zeotropic refrigerant and water, in a air cooled chiller application. In that embodiment, the refrigerant is flowed through the evaporator in a single pass in one direction, while the water is flowed through the evaporator in a single pass in the opposite direction. The inner member preferably is shaped as an elongated cylinder.
In another aspect, the invention includes a method for exchanging heat between a fluid and a refrigerant in a tube(s) and shell heat exchanger, comprising the steps of flowing the refrigerant through an annular passage formed between the opposing surfaces of an elongated tubular member and an elongated inner member contained within the tubular member, where the tubular member is in turn contained within an elongated chamber. The inner member is supported within the tubular member by a plurality of resilient supports which are spaced along the length of the inner member and protrude from the inner member to engage the tubular member. The method also comprises the step of flowing the fluid in the elongated chamber around the outer surface of the tubular member, to effectuate a heat exchange with the refrigerant. Preferably, the refrigerant is a zeotropic refrigerant having significant glide characteristics. The refrigerant and the fluid flow in opposite directions through the heat exchanger, each making only a single pass.
Experimentation has also shown improvements using this invention with evaporators employing a single constituent refrigerant, such as R-22.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only.
The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of the specification, illustrate several embodiments of the invention, and together with the description serve to explain the principles of the invention.